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Re: [gpsd-dev] ABVDM sentences from AIS
From: |
Eric S. Raymond |
Subject: |
Re: [gpsd-dev] ABVDM sentences from AIS |
Date: |
Fri, 16 May 2014 11:11:23 -0400 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
Iván Sánchez Ortega <address@hidden>:
> A bit of background: "AIVDM" is split into the "Talker ID" ("AI") and the
> "Sentence formatter" ("VDM"/"VDO"). An "AI" talker is a "Mobile AIS station"
> (a boat), and "BS" is a "Base Station" (big antenna on ground).
I actually somehow managed not to know this, though I see BS is
supported in gpsd's lexer. Where are AIS talker IDs documented? I'd
like to summarize them in my AIVDM/AIVDO protocol decoding guide.
> As far as I'm aware, with the introduction of NMEA 4.00 the talker ID "BS"
> will disappear and will be replaced by either "AB" or "AD" and maybe "AT" and
> "SA", plus there will be "AN" (buoys) and "AX" (repeaters).
This raises some questions in my mind:
1. You say '"AB" or "AD" and maybe "AT" and "SA"'. What are these different
talker prefixes supposed to mean? I'd like to document them.
2. Where can I read about these and other NMEA 4.00 changes?
> My C skills are not that good, but
> even I can copy-paste that code to support ABVDM/ABVDO.
I've done this, and added recognition of AN and AX too.
> I wonder if the right way to go is to treat **VDM and **VDO messages
> as AIS no matter the talker ID,
That wouldn't play well with the way the lexer is currently written.
It could be done, but I'd need a real user story before adding the
additional complexity.
> and I wonder if having the talker ID in the outputted
> JSON would be of any practical use at this point.
Unclear. I think we can actually deduce fixed/mobile pretty
reliably in other ways.
--
<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>